In the industrial automation field the use of robotized manipulators is known, a gripping clamp for the objects to be manipulated being normally associated with.
The clamps are provided with a body housing the jaws, also called grips or gripping fingers, and the corresponding activating device. The jaws are movable between a first not-operating position or releasing position, where they do not apply any pressure on the piece to be manipulated and an operating position, or gripping position, where they apply a pressure on the piece to be manipulated adequate to provide the workpiece not becoming accidentally free during its movement. The device for activating the jaws can be electric, pneumatic, oleo-pneumatic, etc.
According to the number of the jaws and their movement, they can be clamps having two jaws, which can be parallel, radial or angular, clamps having three jaws, etc.
The present invention relates to the electrically driven clamps with two parallel jaws. Some examples are given in EP-A-2374580, JP-A-2009226506, JP-A-2010094787, U.S. Pat. No. 5,947,539 and WO 03/068456.
A further specification relates to the jaws stroke. On the market clamps with two parallel short- or average-stroke jaws are considered those clamps wherein the jaws have both a stroke shorter than 10-15 mm, and clamps with two parallel long-stroke jaws are considered those clamps whose jaws both have a stroke greater than 10-15 mm, for example 20 mm, 40 mm, 100 mm, 200 mm, etc.
A practical example of an electrically driven clamp with two parallel long-stroke jaws, is constituted of the series HGPLE clamp commercialized by the company Festo AG & Co. KG (HGPLE-25-40-2,8-DC-VCSC-G85).
Other examples are constituted of the clamps series GEH6000 and GEH8000 commercialized by the Sommer-Automatic company, belonging to Zimmer-Group.
Generally, the electric motor is housed in the clamp body and controls the jaw translation, alternately in the two ways, by means of a transmission assembly constituted of gears and a drive belt, or of a worm, which meshes the jaws, or yet a gear wheel which meshes respective racks integral with the jaws, etc.
The manufacturers provide an electronic unit needed for controlling the operations of the electric motor. Such an unit is particularly expensive and complicated to realize and develop and has, among the others, the task of activating the electric motor, inverting the drive shaft rotation to change the translation way of the jaws, interrupting the power supply of the drive shaft when the jaws encounter an excessive resistance in the respective path—so as to avoid overloads—, stopping the motor, etc.
Independently from the technical solution adopted for transmitting the motion from the shaft of the electric motor to the jaws, that is to say independently from the configuration of the transmission assembly, the above described clamps suffer from some not negligible drawbacks.
The most relevant drawback consists in that the electronic unit needed for controlling the electric motor is outside the body of the clamp itself. Usually a proper electric connector is provided on the clamp body for connecting to the outer control unit. In many applications the control unit remains proximal to the clamp, often constrained to the manipulator by its side, and therefore negatively affects the bulks. In particular in many applications the clamp has to be inserted into a seat of the piece to be manipulated and the possible presence of the control unit can remarkably limit the freedom of movement of the clamp itself, meaning that the displacements have to be calculated to take the bulk of the control unit into account.
A further drawback is constituted by the weigh of the control unit. In case such a unit is positioned on the manipulator with its respective clamp, the mass of the control unit negatively affects the dynamical performance of the manipulator.
Yet another drawback of the conventional solutions consists in that the transmission assembly operating the transmission of the motion from the electric motor shaft to the jaws, in case the involved stresses are high or the gears are worn, does not assure the maintenance of the so called gripping center, that is to say it can occur that the jaws do not reach the respective limit positions simultaneously or one of the jaws does not reach its own limit position exactly.